1. Field of the Invention
The present invention relates to methods for fabricating semiconductor devices, and in particular to methods for fabricating capacitors.
2. Description of the Related Art
The development trend in the rapidly evolving integrated circuit industry is toward high performance, miniaturization, and high operating speed. Dynamic random access memory (DRAM) fabrication methods have also developed rapidly. More specifically, shrinking design dimensions is a strategic aim. However, as each memory cell shrinks, a capacitor must maintain a certain charge storage capacity, for example more than 25 fF, to ensure reliable operation of the memory cell.
A DRAM cell typically comprises a transistor and a capacitor. The capacitor is formed by disposing a dielectric material between two electrode plates. The capacitance is represented as C=KA/D, wherein K is the dielectric constant of the dielectric material in the capacitor; A is the electrode area; and D is the distance between two electrode plates. To increase capacitance without enlarging the area occupied by the DRAM cell on the wafer, a high-k dielectric material is used to form the dielectric layer between the electrode plates. Alternatively, growth of HSG silicon (hemispherical grained silicon) on the surface of the top and/or bottom electrode plate is used to increase the surface area of the electrode plates. U.S. Pat. No. 6,300,192 by Kim entitled as “METHOD FOR FABRICATING A DRAM CELL CAPACITOR USING HEMISPHERICAL GRAIN (HSG) SILICON”, discloses forming HSG silicon on the polysilicon plate by performing a seeding method in a stacked capacitor structure. However, this skill is limited to the bottom electrode material, which must be polysilicon for growth of HSG silicon. As metal is needed for the electrode plate, the conventional technology for increasing the surface area of the electrode plate by growing HSG silicon on the polysilicon electrode is not suitable for use in the manufacturing process. Hence, a new method for increasing the surface area of the electrodes to raise capacitance without additional photolithography mask is needed.